HYDRAULIC SWITCHING MECHANISM FOR MOBILE HYDRAULICS, MOBILE HYDRAULIC MACHINE AND VALVE UNIT

摘要

The invention relates to a hydraulic switching mechanism (10) for the mobile hydraulics of, for example, hydraulic excavators, with a valve block, with electrohydraulically activatable valve units for controlling the movement of a working cylinder (6) whose cylinder chambers (ZA, ZB) can be selectively connected to a pump connection (P) for hydraulic fluid, to a tank connection (T) or to one another, and with pre-control valves for activating the valve units, wherein the hydraulic switching mechanism, by means of separate tank valve units (C2, C4) and pump valve units (C1, C3 ) according to the invention, and also a suitable pre-control system (7), makes it possible to achieve not only a directional control valve function but also to achieve a directly controlled and superimposed pre-controlled lowering braking function, a maximum pressure safeguarding of the cylinders and a proportional throttle valve function for the controlled displacement under negative load forces in the direction of movement and braking in an emergency. Furthermore, the invention also relates to mobile hydraulic machines having such a hydraulic switching mechanism and also to valve units therefor.